I have been a Nokia user for some time and got anger and anger with the ever growing bugs on their smartphones (my current N97 is a nightmare). I don't want the newest app or fancy updated OS. Just a bug free phone with the functions I did pay for. And now, instead of continued development must I buy a new phone with another OS from the scratch? Sure... Thanks, but no thanks. I will look for a different brand.

This is a big win for micosfot considering the huge unexplored smart phone market of the future. Is windows can really build a good OS which can give user experince of apple ios and android, then we might saee a real battle in the future.

It is advertised as a power-merge of two giants, but the deal targets a smartphone market - the market, in which these two are giant loosers! Some say it may be: 1+1 yielding more than 2 (synergy effect), but to me it seems like 1+1 yielding less than 1 (looser plus looser yields just a bigger looser!).
The very first moment I'd heard Elop taking the CEO post at Nokia I got a feeling it must be a kind of MS's Trojan horse, and with this co-op anouncement it has just opened up! There are arguments for not choosing android, but choosing WinPhone can help Nokia gain the market only among those who never heard of Windows before the XP version and then fell in coma for the period of Vista being in the market. I bet it's not too big share! Abandoning Symbian is way too fast (or should have been done MANY years ago) now after it got working with touch screens, widgets, etc., and the "ovi" app store gained momentum. There should have been more resources (and Nokia had enough cash for that!) put to MeeGo instead, which works fine on N900 phones. Many liked Nokia for its reliable hardware, and open sourced OS. But they sold hardware design to ST Ericsson (to free themselves to choose whatever hardware is 1st/best on the market), and now opt for WinPhone7 OS - what's left? A logo. How's that differing from HTC, Samsung and the like? It migt be not the coffin nail to Nokia as a company (hard to predict, but rather likely), but it definitely is a coffin nail for the sentiment to Nokia brand.
Bottom line - great deal for MS, and likely a death sentence for Nokia. Sad but true!

I think calling this action the nail in the coffin for Nokia is given Nokia's current course too much credence and chance of success.
I think at this point, we need to stop calling them "smartphones". The iPhone changed all that. The iPhone is really an iPOD Touch that just happens to make phone calls. Most of the "coolness" of the iPhone was already there with the iPOD Touch.
I think the analogy to IBM and Microsoft in the early days of the PC is accurate in some ways, but it is not about what IBM gave away or lost, but to the "birth" of a platform. That same birth is happening again. Nokia came to the conclusion they did not have a viable platform to compete. They may have come to the conclusion that a proprietary platform would not fly in the future. Anyone remember Commodore computers?
Perhaps Android would have been a better choice, but perhaps Nokia doing their homework felt otherwise. While Android is very popular, the number of apps sold -- not available, but units sold, is small.
No ones crystal ball is perfect enough to pick a winner. Android does seem like the safest bet as eventually Apple like the Mac, will become a niche player.

Going to Android will just make Nokia no difference from Samsung, Sony Ericsson and LG. Android may be ruling market of mobile device for a while. Fail to acquire a close partner to grow a better UI and a better product would be an idea going against Nokia's wish. The success of a product isn't just a product itself but the market execution. I certainly wish the relationship between Nokia and Microsoft will breed a new product and even a new market.

It will be interesting to see how long it takes Nokia to get a WinPhone out, whether they put any real pressure on Android and what if anything Nokia does to differentiate itself from Samsung, HTC and etc.

I think Nokia have, probably, just signed their death warrant with this deal. If they wanted an OS they would share with others, they should have continued with Symbian or gone for Google's Android. Instead they did what IBM three decades ago and gave Microsoft a lifeline with little in return. The difference this time is that Microsoft is a late-mover and not a first-mover, so I fail to see what Nokia will get out of it, if at all.